The overall aim of the Project 1 is to develop a fully functional field deployable prototype of a retrospective dosimetry system based on radiation-induced signals in teeth suitable for rapid screening and dose assessment following radiation exposures in the range that could lead to the acute radiation syndrome. More specifically, the system will be useful for responding to events in which large numbers of people have potentially been exposed and there is a need to perform triage to most effectively apply limited medical resources. The technical approaches are based on the use of EPR spectroscopy to quantitatively measure the relative concentration of radiation-induced free radicals that exist perpetually in tooth enamel. The concentration of these radicals is varies in direct proportion to the absorbed dose. The specific experimental approach is based on the progress and insights that we have we have achieved in the initial funding period of the CMCR Centers and with other prior support. The research plan for the renewal period is a combination of improving the techniques established to date and developing additional approaches that may result in substantial improvements in speed, accuracy, and ease of measurements. In essence, the teeth fulfill the role of an endogenous physical dosimeter, with no need for installation and low probability that the dosimetric material (i.e. teeth) will not be present at the time of the exposure. The EPR tooth dosimeter will be fully compatible with the needs for field operation by minimally trained personnel. The detected effects of irradiation require no appreciable time to develop, are stable, and their measurement can provide an immediate estimate of absorbed dose. There is no need for shipment of samples or complex logistics involved in associating samples with subjects for follow-up, which may be especially difficult in the immediate aftermath of a catastrophic event. This physically based measurement is a very effective complement to biologically based dosimetry methods because it is not dependent on biological processes that can affect the development and timing of the responses to radiation, i.e. it is independent of pre-existing and co-existent physiological and pathophysiological processes and does not require time after exposure to develop and or change with time. An independent absolute measurement of absorbed dose may lie particularly helpful in assessing subjects with trauma which may interfere with biologically based assays. Based on these unique characteristics, we believe that the development of this technology is crucial and a valuable component of the CMCR program.